Test this out. Try creating a receiver with perfect route running and repeatedly running digs and outs. I notice that a lot of the time, you don't get any "slowdown" animation for the WR as he makes his cut. So in other words, his SPD, AGI, and ACC ratings are what determines whether he gets open or not.

The problem seems to be that receivers get a "route penalty" too often. In other words, that the penalties on route running kick in at too high a level. Even elite players get these "loss of speed" animations way too often, and it seems like the game would play much better if it was such that these animations largely didn't come into play unless a player was below 80 or so in route running. That would make it so that you couldn't play track athletes who don't have good WR skills, but not such that legitimate WR's can't make speed cuts.

Also, in my tests, it doesn't look like removing the "slow down" animation really hurts the defense all that much. If the DB covering the play has good locomotion attributes (ACC, AGI, SPD), then he will often times either be there to make the tackle right after the catch, or to even break the pass up if it's further downfield.

So it seems to me that EA could fix this issue relatively easily by simply tuning the frequency that these "loss of speed" animations play (and the types that play) when receivers make cuts.